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Thorax:Solid viscus:Heart
The heart is a pyramidal muscular pump responsible for circulation made up of: * Cardiac chambers ** Right atrium (RA), right ventricle (RV), left atrium (LA),left ventricle (LV) * Cardiac valves ** Atrioventricular (AV) valves *** Tricuspid, mitral ** Semilunar valves *** Pulmonic, aortic * Cardiac structure ** Epicardium: Serous visceral pericardium ** Myocardium: Specialized cardiac muscle that forms atrial and ventricular walls ** Endocardium: Thin layer of cells that lines internal surfaces of cardiac chambers and participates in cardiac contraction Position: * Lies obliquely in the thorax with the long axis passing downwards and to the left to the apex * The right sided chambers are anterior and left side are posterior * The interatrial and interventricular septa are in 45 degree to sagittal plane Relations * anteriorly: body of the sternum and adjoining costal cartilages; left lung andpleura (apex) * posteriorly: oesophagus, descending thoracic aorta, azygos and hemiazygos veins, thoracic duct * superiorly: bifurcation of main pulmonary trunk * inferiorly: diaphragm * laterally: lungs, pleura Five surfaces: * Sternocostal surface: RV with the RA on its right side and narrow strip of LV * Diaphragmatc surface: one third RV and two thirds LV * Posterior: almost entirely of LA receiving the four pulmonary vein * Left: LV and portion of LA * Right: RA Three borders: * Right: right atrium * Inferior: mostly right ventricle with small portion of left ventricle * Left: left ventricle with the auricle of the left atrium Right atrium is the chamber in which the systemic blood first returns. * Lies between superior and inferior venae cavae, in front of the left atrium * Medially off the right atrium is an outpouching called the right auricle. This triangular appendage overlies the commencement of the aorta. * The''' sulcus terminalis', ridge on the outside of the heart from the right auricle and SVC down to the IVC, demarcating the separation between these structures. * The '''crista terminalis', is a projection corresponding to the sulcus terminalis * The interior of the right atrium is smooth (origin of sinus venosus), but between the crista and right auricle, the myocardium is project into a series of horizontal ridges which is the pectinate muscle. * Fossa ovalis is shallow saucer shaped depression on the interatrial septum representing the original foramen ovale. * Vascular openings: coronary sinus (left of the IVC, and the septal cusps of the tricuspid valve). The superior venae cavae and inferior venae cavae. Right ventricle receives the blood from the right atrium and pump the blood in to the pulmonary circuit. * The walls are made into a series muscular ridge called trabeculae carneae, that project into the cavity of the ventricle. Papillary muscles (anterior, posterior, septal) project into the lumen of the ventricular walls and holds the attachment of the chordae for the tricuspid valve. ** Anterior papillary muscle: Largest, arises from anterior ventricular wall ** Posterior papillary muscle: Some chordae tendineae arise directly from ventricular wall ** Septal papillary muscle: Most inconsistent * Moderator band: septomarginal trabecula, is a bridge between lower interventricular septum and base of anterior papillary muscle, containing part of the right branch of the conducing bundle. * Cavity of the ventricle continues upwards into the funnel shaped approach to the pulmonary orifice, called infundibulum. Left atrium receives from the blood from the pulmonary circulation. A small bent left auricle projects from its upper border. * Cavity of the left atrium is smooth walled except in the auricle. * Posterior or inflow portion: Smooth-walled, receives four pulmonary veins * Anterior or outflow portion: Continuous with LA appendage, lined by pectinate muscles * Interatrial septum: contains valve of foramen ovale. Left ventricle is the main pump of the blood to the systemic circuit. It is conical in shape with an anteroinferiorly projecting apex and is longer with thicker walls than the right ventricle * Two papillary muscle (anterior and posterior). * Interventricular septum, bulges foward into the cavity of the right ventricle. The upper end of the septal wall is smooth and thin called membranous part of septum. The lower end of is muscular. * Internally, there is a smooth inflow and outflow tracks and the remainder of the left ventricle (mainly apical) is lined by fine trabeculae carnae * Blood flows in via the atrioventricular orifice lined by the mitral valve and flows out passing through the aortic valve into the aorta. * There are two papillary muscles. The anterior is larger. Both are connected by chordae tendineae to each mitral valve cusp. ** anterior (anterolateral) ** posterior (posteromedial) Variant anatomy * double-inlet ventricle: in-flow from both the right and left atria * parachute valve: mitral valve chordae tendinae inserting into a single papillary muscle Valves: collagenous fibrous tissue that guard the blood flow through the heart. Atrioventricular valves are flat and free edges are serrated. The outflow valves are cup shaped and free edge contains a central fibrous nodule. These close edge to edge on closure. * Tricuspid valve: located at the atrioventricular orifice. Has three cusps (anterior, posterior, septal) and attached to the base of the fibrous atrioventricular ring. These receive chordae tendineae, collagenous cords which diverge from papillary muscle and prevent cusp from inverting. * Pulmonary valve: a three semilunar cusps (left, right, anterior) of the pulmonary valve are attached at the junction of the infundibulum and the commencement of the pulmonary trunk. * Mitral valve: two leaflet (anterior and posterior), the base of the anterior cusp and posterior cusp attached with the fibrous atrioventricular ring, at 1/3 and 2/3 respectively. Free edge attached to papillary muscle via chordae. The anterior cusp is thicker and more rigid. * Aortic valve: three semilunar cusp (left, right, posterior or non-coronary) located at the entrance of the ascending aorta. Nerve innervation: The heart has extrinsic and intrinsic innervation, which allows the heart to continue beating if the nerve supply to the heart is disrupted (e.g. in cardiac transplant). * Extrinsic: The heart receives innervation from both the superficial and deep cardiac plexuses, which have both parasympathetic (from vagus nerve) and sympathetic inputs, which provide post-ganglionic fibres to the sinoatrial (SA) and atrioventricular (AV) nodes, as well other parts of the cardiac conduction system. * Intrinsic: Cardiac myocyte conduction spreads through the heart from myocyte-to-myocyte starting the SA (pacing) node. Each part of the cardiac conduction system has its own intrinsic pacemaker. If higher pacing centre (e.g. SA node) is damaged a lower pacing centre (e.g AV node) takes over. Blood supply Arterial: coronary artery. For example left ventricle is via * left anterior descending artery: supplies free wall and most of the papillary muscles * left circumflex artery: supplies free wall Venous: cardiac veins Lymphatic supply Various lymphatic plexuses drain into a right cardiac collecting trunk (draining to anterior mediastinal nodes) and a left cardiac collecting trunk (draining to tracheobronchial nodes and onto paratracheal nodes). Normal Variation * aberrant location of the heart in dextrocardia and situs inversus * Eustachian valve: remnant valve of the IVC * Thebesian valve of the coronary sinus * patent foramen ovale